The solubility of benzoic acid (HC7 H5 O2) is 0.34 g / 100 mL in water at 25^∘ C and is 10.0 g /

step 1 Start with benzoic acid, which is non -polar. We're told that we have 0 .34 grams per 100 mil li

The solubility of benzoic acid (HC7 H5 O2) is 0.34 g / 100...

The solubility of benzoic acid $\left(\mathrm{HC}_{7} \mathrm{H}_{5} \mathrm{O}_{2}\right)$ is $0.34 \mathrm{g} / 100 \mathrm{mL}$ in water at $25^{\circ} \mathrm{C}$ and is $10.0 \mathrm{g} / 100 \mathrm{mL}$ in benzene $\left(\mathrm{C}_{6} \mathrm{H}_{6}\right)$ at $25^{\circ} \mathrm{C}$. Rationalize this solubility behavior. (Hint: Benzoic acid forms a dimer in benzene.) Would benzoic acid be more or less soluble in a 0.1-M NaOH solution than it is in water? Explain.

The solubility of benzoic acid $\left(\mathrm{HC}_{7} \mathrm{H}_{5} \mathrm{O}_{2}\right)$
is $0.34 \mathrm{g} / 100 \mathrm{mL}$ in water at $25^{\circ} \mathrm{C}$ and is $10.0 \mathrm{g} / 100 \mathrm{mL}$ in
benzene $\left(\mathrm{C}_{6} \mathrm{H}_{6}\right)$ at $25^{\circ} \mathrm{C}$. Rationalize this solubility behavior. (Hint: Benzoic acid forms a dimer in benzene.) Would benzoic acid be more or less soluble in a 0.1-M NaOH solution than it is in water? Explain.

Key Concepts

Solvent Polarity

The polarity of a solvent plays a crucial role in dissolving substances. Water is highly polar, which means it tends to dissolve polar substances well, but nonpolar compounds or molecules with significant nonpolar character may not interact effectively with water molecules. In contrast, benzene is nonpolar and dissolves nonpolar or weakly polar molecules more readily, influencing the solubility behavior of organic compounds.

Intermolecular Hydrogen Bonding

Intermolecular hydrogen bonding is important for the solubility of molecules. Benzoic acid has both polar functional groups and aromatic parts, allowing it to engage in hydrogen bonding. In polar solvents like water, hydrogen bonds form between solute and solvent molecules, while in nonpolar solvents, the hydrogen bonding may lead to self-association (or dimer formation), which in turn affects solubility.

Dimerization

Dimerization refers to the process where two molecules associate through intermolecular forces, such as hydrogen bonding, to form a dimer. In nonpolar solvents like benzene, benzoic acid molecules can form dimers, which are more soluble than monomers in that medium. This explains the increased solubility of benzoic acid in benzene compared to water.

Acid-Base Reactions

The solubility of benzoic acid in basic solutions such as a NaOH solution is enhanced due to acid-base reactions. Benzoic acid reacts with hydroxide ions to form its conjugate base, the benzoate ion, which is more soluble in water than the undissociated acid. This reaction transforms a poorly soluble acid into a water-soluble salt, increasing its overall solubility in basic environments.

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